I have an argument as to why we should legalize pot, that's somewhat unconvential from the traditional run-of-the-mill pro-pot arguments.
First it's important to understand where most pot you get comes from, Mexico and other countries near there, but mostly Mexico. Specifically, Mexican drug cartels, since they're the ones who profit off selling the stuff (along with other illegal drugs).
Now the thing about these drug cartels is that they're violent, ruthless, and corrupt. They maintain a lot of power through large sums of money, which they can use to economic advantage and bribery/corruption in the government. If those methods don't work then they resort to methods of fear; murdering those that stand in their way. The violence generated from their existence is horrific for many who live in Mexico and it is a primary motivation for many families to immigrate out of their Mexico into the U.S. where it is safer to live. Now of course many immigrant families don't have the money and time to wait for legal access into the U.S. and thus they immigrate illegally.
Now currently in the U.S. many people are sitting in prison for drug related offenses; smoking pot and or other drugs can get people locked up for a significant amount of time, and this large number of arrested people uses up a lot of tax payer money. Not to mention, it's just plainly cruel knowing how otherwise innocent people are suffereing the horros of prison.
Also those who do purchase illegal drugs of the street are (at least to an extent) unknowingly supporting drug cartels in power; the local vendors who sell drugs on the street aquire their drugs that come from the supplies of cartels in Mexico. Thus buying street drugs gives the cartels more power.
Now, if we legalize pot (and other drugs) then several things can happen; the cartels will lose a lot of power, giving the Mexican government a better edge of destroying them; illegal immigration will lessen as Mexican families will start to see a less hostile and violent life in Mexico and thus less incentive to immigrate; pot smokers won't have to suffer the horros of prison and prion crowding will lessen a lot; drugs can be produced here in the states, out of the hands of the cartels; companies producing those drugs will need workers, thus more jobs in the economy.
This can aslo be said og many other drugs as well, pot just being one of the biggest and most safest of all drugs.